The proposed research has as its overall goal an analysis of the relationship between stimulus control and response differentiation. Specifically an attempt will be made to define and analyze the conditions under which graded stimulus changes yield correlated changes in the topography of the response, a relationship between a stimulus and response dimension referred to by Skinner as a continuous repertoire. Most previous attempts to obtain continuous repertoires under laboratory conditions have yielded negative or inconclusive results. However, pigeons trained to peck the key below a spot which appears during training in only a limited number of positions will readily peck a novel key when the spot appears above it for the first time. A series of experiments are planned to study the effect of variables such as the degree of training, number of points of correspondence between the stimulus and response dimensions established during training, and characteristics of the particular spot-key relationship tained, on the development of continuous repertoires.